The invention relates to tactical or guided missiles, and more particularly, to electronic safe arm and fire devices.
FIG. 1 illustrates a typical guided missile. Guided missile 10 can have several different sections. For example, guided missile 10 can include a seeker section 11, a guidance section 12, a midbody section 13, a propulsion section 14, and a control section 15. Most missiles have one or more warheads that are used to inflict damage on a target. The warhead or warheads can be positioned to optimize the damage to the target. For example, a first precursor warhead can be positioned in the guidance section 12 and a second main warhead can be conveniently positioned in the midbody (or main warhead) section 13. The missile can use sensors or switches to determine contact with an object external to missile 10. These sensors or switches can be positioned in the seeker section 11 or other forward section of the missile.
An electronic safe arm and fire (ESAF) device is a standard feature on most guided missiles today. As its name suggests, an ESAF device is used to safely arm and trigger a guided missile warhead(s). An ESAF device should ensure that the missile has been launched, has traveled a minimum safe distance, and is operating properly before the warhead or warheads are armed or fired. If the missile has multiple warheads, the ESAF device should fire the warheads at delayed intervals. The missile launcher has to be confident that the warhead or warheads will detonate at the proper time.
As with the development of any new technology, the actual implementation of ESAFs has been more difficult than expected. One reason for the difficulty is that the standards for ESAFs are usually set by the Federal Government, and very often, these standards have many requirements that must be satisfied. Another reason is that there are several different types of tactical weapons and each one uses different signals and/or signal interfaces.
One example of a tactical weapon is the Hellfire II missile. The Hellfire II missile uses asynchronous serial data and single ended interfaces (i.e., one line signals) to transmit information to the ESAF device. The Hellfire II missile has a signal that is activated when the missile is launched. This signal is usually referred to as the "umbilical separation" signal. After the Hellfire II missile has been launched, a guidance section directs (or guides) the missile. A signal from the guidance section (the "fuze data" signal) indicates whether the guidance section is operating properly. An accelerometer is useful to indirectly measure the distance between the launcher and the missile ("the separation distance").
The Hellfire II missile has two warheads that are used to inflict damage on a target. The Hellfire II missile has crush switches that indicate whether the missile has contacted an object that may or may not be the target. The crush switches generate an impact signal that is used to determine when, if ever, to detonate the warheads.
Another example of a tactical weapon is the Longbow missile. The Longbow missile is very similar to the Hellfire II missile in that the Longbow missile uses asynchronous serial data and single ended interfaces (i.e., one line signals) to transmit information to the ESAF device. The Longbow missile has an umbilical separation signal, a faze data signal, and an impact signal. An accelerometer is useful to indirectly measure the separation distance.
A third example of a tactical weapon is the BAT submunition. The BAT submunition uses asynchronous pulse width modulated serial data and differential interfaces (i.e. two line signals) to transmit information to the ESAF device. The BAT submunition has an umbilical separation signal, a fuze data signal, and an impact signal. The BAT submunition falls away from a launch platform. The BAT submunition does not accelerate (or take-off) in the same way as the Hellfire II missile or the Longbow missile. For this reason, a differential pressure signal is used to calculate the separation distance.
A fourth example of a tactical weapon is the Javelin missile. The Javelin missile uses synchronous data and differential interfaces (i.e., two line signals) to transmit information to the ESAF device. While the Javelin missile does not have an umbilical separation signal, the Javelin missile has other signals (e.g., a fin lock signal) that are useful to detect whether the missile has been launched and exited its launch tube. The Javelin missile has a fuze data signal and an impact signal. An accelerometer is useful to calculate the separation distance. The Javelin missile requires two additional functions from the ESAF. These include firing the launch motor and flight motor.
ESAFs are usually lighter and smaller than their mechanical counterparts. ESAFs have arming switches that correspond to a mechanical mechanism such as a spring or a gear. Magnavox and EDI were the first companies to develop ESAFs for implementation into tactical missiles. The ESAFs built by Magnavox and EDI are built for a particular missile type using a missile specific electronics module and a set of application specific integrated circuits (ASICs).
As indicated above, and further indicated below, different missiles launch and operate differently. The various missiles come in different sizes and use different power and signal interfaces. Consequently, conventional ESAFs designed for one missile type cannot be used for another missile type. For example, a module and an ASIC designed as an ESAF for a Hellfire II missile can not be used in a BAT submunition because the BAT missile is a different size and uses asynchronous pulse width modulated serial data and a differential interface. In addition, the BAT submunition uses a differential pressure signal, and not an accelerometer, to measure separation distance.
If the Federal Government's guidelines for a missile or a missile's ESAF change, the manufacturer has to develop a new electronics module and a new ASIC. ASIC devices are expensive and time consuming to make. There is a need for an ESAF device that is readily configurable to different or new missile types, but that is inexpensive and relatively easy to make. The device should provide built-in tests and redundancies that are flexible enough to accommodate new or different guidelines. It is not a simple task to build an ESAF device for multiple missile types. An ESAF device having inputs, outputs, and circuits for every possible missile type would be prohibitively large and expensive to make.